1. Field of the Invention
The present invention is directed to liquid filter cells in liquid filtration systems. In particular, the present invention is directed to a method and system for the removal of fouling and clogging material in a filter media support structure in a liquid filter cell.
2. Description of Related Art
Gravity or pressure liquid filter systems often employ filter cells with filter media zones or zones to remove suspended contaminants, such as dirt particles, from a feed liquid. The filter cells operate to remove suspended contaminants by allowing the liquid, oftentimes water, to flow through a filter media zone. As the liquid passes through the filter media zone, the contaminants are collected in the filter media. The filtered liquid is then removed via an underdrain or collection system for further downstream processing.
The filter media is often comprised of a granular material. For this reason, the filter media must be supported, in some manner, in order to prevent the filter media material from passing with the filtered liquid through the underdrain or collection system. Filter media support structures, or media retainers, are designed to allow the filtered liquid to flow through to the underdrain, while prohibiting the filter media or other treatment material from passing to the underdrain or collection area. Filter media support structures either contain gravel or are gravel-less. Existing filter media support structures commonly comprise material with slots, perforations, apertures, or other geometrically-shaped openings; plastic or other material chemically held or sintered together; or other material manufactured to preclude the passage of filter media to the underdrain or collection area. Media support structures of either the gravel or gravel-less type are prone to fouling and clogging by biological matter and chemical scaling, thereby blocking the flow of filtered liquid. As a result, the pressure drop across the media support structure will increase and may ultimately cause the filter cell to fail when the headloss across the system exceeds the design pressure drop. The underdrain itself may be considered part of the filter media support structure and may itself be in need of cleaning from scaling or fouling.
For this reason, routine monitoring of the pressure drop across the filter media support is required. A number of methods are well known and acceptable, including the methods disclosed in United States Patent Application Publication No. 2007/0175832 to Roberts. Using one of such well known methods, once the pressure drop is determined to be unacceptable for operation, maintenance of the media support structure must be performed.
Filters are commonly backwashed periodically to remove collected contaminants and debris from the filter media. One method of cleaning media support structures is adding chemicals capable of removing fouling and clogging material to the backwash liquid. The backwash liquid, now in a solution with the chemical(s), is then introduced to the filter cell to some height above the filter media zone, completely submerging the filter media. The solution may then be agitated and allowed to soak all components of the filter cell for several hours until the solution is removed. Another common method requires the entire removal of filter media, thereby exposing the media support structure. The media support structure is then sprayed and/or soaked with cleaning solution.
Both above-identified methods can be problematic. Often times, exposing the filter media zone to chemicals or cleaning agents can damage the filter media, particularly in filter cells which utilize biologically active filter media zones. Therefore, such systems are incompatible with maintenance procedures that submerge the filter media zone in a cleaning solution. Additionally, these types of procedures require a large amount of cleaning solution. Maintenance procedures requiring complete removal of the filter media zone are time consuming and can result in prolonged disruptions in operation. If removed or exposed to cleaning solutions, biologically active filter media zones may require several weeks to reach optimal levels of biological activity required for filter operations.
Therefore, it is desirable to have a method and system for cleaning a media support structure in a filter system, which employs a filter media zone, which method and system overcome the above-described deficiencies.